Heat-insulating body

ABSTRACT

The invention concerns a heat-insulating body comprising: a) a pulverized hard foamed plastics material and optionally an inorganic porous material; and b) a foil enveloping component a). The foil enveloping component a) is evacuated and then hermetically sealed.

BACKGROUND OF THE INVENTION

It is known that heat insulating bodies (vacuum panels) can bemanufactured from a porous material and a gas-tight sheet which providesan all-round cladding, the "hollow space" formed by the porous materialbeing evacuated. The porous material may consist either of an expandedbulk material, or of a rigid foamed material, however. The sheet usuallyconsists of combinations of several layers, with different functionsbeing performed by the different layers, such as a diffusion barrier tovarious gases and mechanical reinforcement.

Most commercially available vacuum panels have a core of inorganic bulkmaterial, which is usually silicate-based.

EP-B-188 806 describes rigid foamed materials based on polyurethane(PUR) as a filler material for vacuum panels. The problem with thisprocess is to achieve the requisite open cellularity by the preciseselection of the formulation and by adhering to defined processparameters, since PUR rigid foamed materials are predominantly of closedcell structure. The outgassing of volatile constituents such as amines,foaming agents, and possibly monomers also, constitutes another problemwhen using PUR rigid foamed materials as a support material for vacuumpanels.

On the other hand, one advantage of rigid PUR foamed materials comparedwith porous inorganic bulk materials is their accurate sizing asfinished vacuum panels, as well as their dimensional stability.

Surprisingly, it has now been found that an excellent support materialfor vacuum panels can be produced in an economical manner by producing aporous bulk material by pulverising rigid foamed materials andprocessing this bulk material--similarly to porous silicate bulkmaterials--to form vacuum panels. In this connection rigid foamedmaterials are preferably used which arise in the recycling of valuablesubstances, and the PUR foamed material which arises on the recycling ofrefrigerators is particularly preferred in this respect.

SUMMARY OF THE INVENTION

The present invention thus relates to a heat insulating body consistingof

a) a rigid foamed plastic material comminuted to a powder and optionallyan inorganic porous material, and of

b) a sheet which clads component a)

wherein the sheet which clads component a) has been evacuated and thenhermetically sealed.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention it is preferred that

the foamed plastic material to be comminuted is a polyurethane foamedmaterial which preferably originates from the process of recycling oldrefrigerators,

the foamed plastic material powder has a particle size of 0.01 mm to 1mm,

before being clad with the sheet, the foamed plastic material has beenfreed from volatile constituents by heating at temperatures from 50 to250° C., preferably at 120 to 200° C., optionally under low pressure,

before being clad with the sheet, the foamed plastic material powder ispre-pressed at pressures from 0.5 to 5 bar, preferably 1 to 3 bar, and

a multilayer sheet, preferably a polyethylene/aluminium sheet or apolyethylene/polyvinyl alcohol sheet, is used as the cladding sheet,

porous silicates are used as the inorganic porous material.

All known sheets, e.g. combination sheets such as those which are alsoused in the production of commercially available vacuum panels, can beused for the vacuum panel produced according to the invention. Thefollowing may be cited as examples: a combination of polyethylene sheetwith polyvinyl alcohol sheet or polyethylene sheet with aluminium sheet.

In principle, all rigid foamed plastic materials are suitable as foamedmaterials to be used according to the invention. Rigid polyurethanefoamed materials are preferred. Even though the sheets used for vacuumpanels are already highly impermeable to gases, nevertheless they do notconstitute a gas or vapour barrier. In particular, water vapour whichpenetrates can have an adverse effect on the vacuum and thus on the heatinsulating properties of the vacuum panel. In order to prevent this,vapour-absorbing substances, such as those based on silicate or aluminafor example, can be used conjointly according to the invention inamounts from 10 to 90% by weight, preferably 20 to 50% by weight.

Comminution of the rigid foamed material can be effected according tothe invention by milling, grinding or attrition; larger pieces of foamedmaterial may also easily be crushed if necessary.

The fineness of the porosity can be adjusted according to the invention,firstly by the intensity of the milling process and secondly by thefineness of the cell structure of the foamed material to be pulverised.

Pre-pressing of the foamed material powder at pressures from 0.5 to 5bar, preferably 1 to 3 bar, may be advantageous according to theinvention, the pressed article then being processed later to form thevacuum panel.

Porous silicates are preferably used as the inorganic porous materialwhich is optionally to be used according to the invention. The inorganicporous material is optionally used conjointly in an amount of 0.1 to 80%by weight, preferably 20 to 50% by weight, with respect to the rigidfoamed plastic material which is comminuted to powder.

EXAMPLE OF APPLICATION

1000 g of PUR rigid foam powder--obtained from a dismantled old coolingappliance by pulverising the foamed material contained therein--waspre-pressed at 2.5 bar. The pressed article about 2 cm thick which wasthus obtained was cut to the dimensions 40×40 cm after drying for 2hours at 100° C. and subsequently clad with a sheet consisting of thelayers:

polyethylene/polyvinyl alcohol/polyethylene.

The "bag" filled with PUR powder which was thus obtained was evacuateddown to 0.001 bar. The edges of the sheet were welded under vacuum. Thevacuum panel thus obtained had a thermal conduction coefficient λ of 10mW/°Km.

What is claimed is:
 1. A heat insulating body comprisinga) a rigidfoamed plastic material comminuted to a powder and optionally aninorganic porous material, wherein said powder has a particle size offrom 0.01 mm to 1 mm, and of b) a sheet which clads component a),wherein the foamed plastic material powder is pre-pressed at pressuresof 0.5 to 5 bar and, prior to being clad with the sheet, has been freedfrom volatile constituents by heating at temperatures from 50 to 250° C.and, optionally, under a low pressure, and wherein the sheet which cladscomponent a) has been evacuated and then hermetically sealed.
 2. Theheat-insulating body according to claim 1, wherein the foamed plasticmaterial to be comminuted is a rigid polyurethane foamed material. 3.The heat-insulating body according to claim 1, wherein a multilayersheet, is used as the cladding sheet.
 4. The heat-insulating bodyaccording to claim 3, wherein said multilayer sheet is apolyethylene/aluminum sheet.
 5. The heat-insulating body according toclaim 3, wherein said multilayer sheet is a polyethylene/polyvinylalcohol sheet.
 6. The heat-insulating body according to claim 1, whereinporous silicates are used as the inorganic porous material.
 7. Theheat-insulating body according to claim 1, wherein said temperatureranges from 120 to 200° C.
 8. The heat-insulating body according toclaim 1, wherein said pressure ranges from 1 to 3 bar.